1. Technical Field
The present invention relates to a load distribution technique for a media gateway control function (MGCFs) in the transition from a legacy network to an Internet protocol multimedia subsystem (IMS) network. The legacy network is an existing network for providing telephone service in public switched telephone networks (PSTN).
2. Description of the Related Art
In telephone networks such as PSTN and integrated services digital networks (ISDNs), a method for bypass routing of signaling messages is a countermeasure for congestion. For example, Japanese Unexamined Patent Application Publications No. 2001-333114, No. 2003-309650, and No. 2002-290551 disclose a method for controlling calls using a traffic control system (TCS), and a bypass method in which an interface unit between an existing legacy network and an Internet protocol (IP) network notifies the legacy network of congestion to instruct that messages be routed via a bypass. In those methods, the legacy network is instructed to perform bypass routing. In the legacy network, bypass routing is taken into account and appropriate processing is performed accordingly. Therefore, legacy network carriers and IMS network carriers are different, and the above methods are not suitable if the legacy network takes no additional functionality or bypass routing into account.
In the related art, a concentration of calls in disasters, which is assumed to be a main cause of congestion, is controlled by a device for managing an entire network.
Such a control system is not suitable for an environment with coexistence of multiple carriers/domains.
Due to the existence of multiple IMS network managers including an MGCF unit (hereinafter referred to as an “MGCF”) and legacy network managers including a toll switch, a large amount of time and labor is required for such managers to work together to deal with congestion. Since legacy networks are expected to be scaled down in the future, it is desirable to avoid upgrade of existing legacy network infrastructures with a large amount of investment. Further, it is not practical in view of cost to provide IMS network infrastructures in which the overall operating performance of MGCFs is too high. It is therefore desirable that each IMS network manager not invest too much in infrastructure and develop effective countermeasures for congestion without interfering with other networks.